1. Field of the Invention
The present invention relates to a process for stopping continuous polymerization whereby the proceeding of polymerization reaction can be stopped in a short time and be resumed in a short time in the continuous polymerization of methacrylic acid ester polymers and the like.
2. Description of the Related Art
There have been recently adopted continuous bulk polymerization processes or continuous solution polymerization processes in which raw material monomers, a polymerization initiator and the like are continuously added to a polymerization reaction vessel for production of methacrylic acid ester polymers, acrylic acid ester polymers, a polystyrene, an acrylonitrile-butadiene-styrene resin (ABS) or the like.
A production of methacrylic acid ester polymers such as a polymethyl methacrylate (PMMA) by the continuous bulk polymerization process in which methacrylic acid ester-based monomers such as methyl methacrylate (MMA) and a polymerization initiator are continuously fed in a polymerization reaction vessel is described in U.S. Pat. No. 5,728,793.
When the polymerization reaction of MMA and the like is carried out by the continuous bulk polymerization process, PMMA, a reaction product, is taken out from a reaction vessel as viscous polymerization liquid (hereinafter referred to as “polymerization syrup”), then introduced into, for example, a degas extruder to separate and remove unreacted monomers and further pelletized, for example, by a pelletizer, and provided as a raw material of various PMMA products.
At production of the above-mentioned PMMA, when trouble is happened at a degas extruder or a pelletizer which are disposed at the downstream side of a polymerization syrup flow from the reaction vessel, or when inspection and the like are carried out at the above-mentioned downstream side, it is required to stop the influx of polymerization syrup to the downstream side.
As a method of stopping the influx of polymerization syrup to the downstream side, there are methods of flowing polymerization syrup into a storage tank capable of storing polymerization syrup and of stopping polymerization reaction at the upstream side.
Since the period capable of stopping the polymerization reaction is dependent on the volume of a storage tank in the former method, the storage tank with a large volume are required for an adequate time for inspection, repair and the like, and it is technically very difficult to preserve the polymerization syrup with preventing polymerization in the storage tank. Further, the polymerization syrup collected in the storage tank also may not be reused due to thermal polymerization and the like at storage.
On the other hand, in the process of stopping polymerization reaction at the upstream side, usually, the feed of a polymerization initiator to a polymerization vessel is stopped and the polymerization inhibitor together with an MMA monomer is fed to substitute the inside of the reaction vessel with the MMA monomer containing the polymerization inhibitor. Consequently, a significant time is necessary for stopping the polymerization reaction through the above procedure, and the influx of much polymerization syrup to the downstream side cannot be immediately stopped when it is necessary. Further, when resuming the polymerization reaction, a substitution of the MMA monomer containing the polymerization inhibitor with a MMA monomer containing a polymerization initiator is required and, a significant time is required for resumption of the polymerization reaction.